Many parts of the southern half of the UK are likely to exceed 30°C and may even reach 34°C in some places, by Friday.

Away from the northwest, where a series of fronts are bringing rain and cloudier weather to parts of Scotland and Northern Ireland, the weather is fine and dry. The settled conditions are allowing temperatures to build day-on-day with the hottest temperatures expected to be reached by Friday for many.

Met Office Deputy Chief Meteorologist, Jason Kelly, said; “The heat is a result of a mix of home-grown warming due to a high pressure over the southern half of the UK, as well as a south westerly airflow bringing warm air, which has been over the continent through the week, across the country.

“This is the first spell of hot weather this year and it is unusual for temperatures to exceed these values in June. Some areas may see warm nights with minimum temperatures expected to be in the high teens or even low 20°Cs overnight, especially in urban areas such as London.”

Heatwave criteria

A UK heatwave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold. The threshold varies by UK county.

Although some parts of England may perhaps meet these heat wave criteria it looks like this spell of warm weather will be relatively short-lived. Milder conditions look likely to return later in the weekend with temperatures trending back to around average for June as we see cooler air push across the country from the northwest.

It is still relatively unusual for temperature to reach the mid 30°Cs in June and you have to go back to 1976 for the highest recorded June UK temperature (records date from 1884). 35.6°C was reached at Southampton Mayflower Park on 28th June 1976.

A Level 3 Heat-Health Alert has been issued for the much of the South East and eastern England, with a Level 2 Alert in place for the South West and East Midlands, with a Level 1 Alert for the West Midlands and northern England.

Agostinho Sousa, Head of Extreme Events and Health Protection at the UK Health Security Agency, said: “Temperatures are forecast to reach 30°C in some parts of the south on Friday and we want everyone to enjoy the hot weather safely when it arrives and be aware of good health advice for coping with warmer conditions.

“During periods of hot weather, it is especially important to keep checking on those who are most vulnerable, such as older people and those with heart or lung conditions. Make sure to look out for signs of heat exhaustion and follow our simple health advice to beat the heat.”

Looking ahead

A cold front will push across the country from the north as we go through the weekend bringing a return to average temperatures for most. However, there is some uncertainty around how quickly this front will move south and therefore how long the highest temperatures will remain. Areas in the far South East are currently expected to hold on to the warmth the longest, with highs of 29°C in East Sussex and Kent possible on Saturday. 

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Climate change

Dr Mark McCarthy is the head of the Met Office National Climate Information Centre. He said: “Climate change has increased the average temperature of UK summers, and it is also increasing the likelihood of experiencing more extreme temperatures during hot spells and heatwaves.

“Reaching 34°C during June is a rare, but not unprecedented, event in the historical climate records for the UK. But if it should happen this week it would be notable that it would have occurred on three days during the last six Junes.” The other days being 21 June 2017 and 29 June 2019.

Before that the only June exceedances - when England saw a number of stations reach 34°C or higher - were 3 June 1947, 29 June 1957, and 26-28 June 1976: a notoriously hot summer.

An increase in the frequency, duration, and intensity of extreme high-temperature events and heatwaves over recent decades is linked to the observed warming of the planet and can be attributed to human activity. Previous Met Office research has shown that the frequency of high-temperature extreme weather events outnumbers low-temperature extremes by about nine to one.